Nortel Networks NN47200-503 manual Igmp snooping

46An Introduction to IP Routing Protocols

—The stack will continue to run normally with the base unit controlling Layer 3 and DRP functionality.

—If the non-operational non-base unit does not rejoin the stack, no Layer 3 or DRP functionality will run on it.

IGMP snooping

The Nortel Ethernet Routing Switch 5500 Series can sense Internet Group Management Protocol (IGMP) host membership reports from attached stations and use this information to set up a dedicated path between the requesting station and a local IP Multicast router. After the pathway is established, the Nortel Ethernet Routing Switch 5500 Series switch blocks the IP Multicast stream from exiting any other port that does not connect to another host member, thus conserving bandwidth. The following section describes how Nortel Ethernet Routing Switch 5500 Series switches provide the same benefit as IP Multicast routers, but in the local area.

IGMP is used by IP Multicast routers to learn about the existence of host group members on their directly attached subnets (see RFC 2236). The IP Multicast routers get this information by broadcasting IGMP queries and listening for IP hosts reporting their host group memberships. This process is used to set up a client/server relationship between an IP Multicast source that provides the data streams and the clients that want to receive the data.

By default, unknown multicast traffic is flooded to all ports in a VLAN. In situations in which there is a multicast transmitter that is not doing IGMP and there are no multicast receivers, the traffic transmitted by the transmitter is flooded.

The CLI commands for IGMP allow the sending of all unknown multicast traffic to IGMP static router ports only. This traffic will not be forwarded to dynamically discovered m-router ports. If it is desirable to forward unknown unicast traffic to certain ports only, those ports can be set as static m-router ports.

•When disabled, the Nortel Ethernet Routing Switch 5500 Series switch treats unknown multicast traffic as it does broadcast traffic (flood). This is the default behavior.

•User settings for the Unknown Multicast No Flood feature is stored in NVRAM. In a stack, if settings on different units differ, the Base Unit setting will take precedence. This feature can be enabled or disabled at any time.

•Nortel Networks recommends this feature be enabled when IGMP snooping is enabled.

Nortel Ethernet Routing Switch 5500 Series

Configuration-IP Routing Protocols

NN47200-503 03.01 Standard

5.127 August 2007

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